LAMENESS IN THE FORE LEG 65 



structures, and it then becomes necessary to administer an ex- 

 pectant treatment, observing general surgical principles and pro- 

 viding in so far as possible for the comfort of the patient. 



Scapulohumeral Arthritis. 



Anatomy.— The scapulohumeral joint is an enarthrodial (ball 

 and socket) joint wherein the ball or humeral articulating head 

 greatly exceeds in size the socket or glenoid cavity of the scapula. 

 The capsular ligament surrounding this joint is very large and 

 admits of free and extensive movement of the articulation. There 

 exist no lateral or common ligaments jointing the scapula and 

 humerus as in other joints, but instead the tendinous portions 

 of muscles perform this function. The principal ones which are 

 attached to the scapula and humerus that act as ligaments are 

 the supraspinatus (antea-spinatus), infraspinatus (postea- 

 spinatus) biceps-brachii (flexor brachii) and subseapularis mus- 

 cles. 



Etiology and Occurrence. — Inflammation of the scapulohum- 

 eral articulation results from injuries of various kinds, including 

 punctures which perforate the joint capsule, bruises from col- 

 lars, metastatic infections and involvement as a result of direct 

 extension of infectious conditions situated near the joint. 



Classification.— Acute arthritis may be septic or aseptic, and 

 there seems to be a remarkalile tendency for recovery in cases 

 of septic arthritis involving this joint in the horse. 



Chronic arthritis with destruction of articular surfaces and 

 ankylosis, is seldom observed. It is only in cases of severe in- 

 jury, where the articular portions of the bones are damaged at 

 the time of infliction of the injury, and where the articulation 

 remains exposed for weeks at a time, together with immobility 

 of the parts because of attending pain, that permanent ankylosis 

 results. 



Scapulohumeral arthritis may result then from infections, local 

 or metastatic; from injuries, such as contusions of various kinds; 

 from wounds, which break the surface structure or perforate 

 the joint capsule; or from luxations. 



